I have the AT&T 8525, which is similar to the Mogul in that it is made by HTC and has a sliding keyboard:
I've only had it 5 days so far. My preliminary thoughts:
* Battery life is not very long. I have to charge it every day. (Yesterday, I forgot to turn off MSN Messenger, and it ate a full battery overnight, so don't do that.)
* Phone functions could be better. I'm used to a regular phone, with real keys, and the touchscreen pad is a litte annoying. (You can't really slide out the keyboard if you're out and about.)
* The PDA functions are great. The Pocket PC is fast, and there is tons of software available for download.
* The keyboard is very usable. I had a Blackberry 7230 and the keyboard for the HTC is much better. I've only had it 5 days, so I can't speak for the durability.